1. Field of Invention
The invention concerns cast tube-joint pieces used in trusswork constructions constructed out of steel tubes. Such constructions are used, e.g., in oil drill towers and in the support legs of offshore oil drill rigs.
2. Description of Prior Art
At the branching points in large trusswork constructions made of steel tubes particular cast joint pieces are frequently used. In these joint pieces there is a branch for each tube to be joined. Each tube to be joined is welded to the end of its associated branch endwise. By use of cast joint pieces, considerable advantages are obtained as compared with the use of welded joints alone:
The welding work is easier, because the joints are aligned end to end. The tube ends to be joined may also be machined ready in advance.
The welding joints are located in areas in which they are not subjected to high strains.
By casting, the angle points can be rounded gradually, which is necessary to eliminate risky tension peaks.
By means of the casting technique, the critical joint areas can be made stronger at the exact location where strength is needed.
In rectangular constructions, it is possible to use identical joint pieces for the various branching points. However, in the case of conical tower constructions, the joint angles of the tubes vary based on the type of branching points. Thus for one such conical tower construction, it is necessary to cast a great number of different types of joint pieces, which of course makes the unit costs of the different joint pieces quite high.